[PATCH] libgcc: Move cfa_how into potential padding in struct frame_state_reg_info

[Florian Weimer via Gcc-patches]

On many architectures, there is a padding gap after the how array
member, and cfa_how can be moved there.  This reduces the size of the
struct and the amount of memory that uw_frame_state_for has to clear.

There is no measurable performance benefit from this on x86-64 (even
though the memset goes from 120 to 112 bytes), but it seems to be a
good idea to do anyway.

libgcc/

        * unwind-dw2.h (struct frame_state_reg_info): Move cfa_how member
        and reduce its size.

---
 libgcc/unwind-dw2.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/libgcc/unwind-dw2.h b/libgcc/unwind-dw2.h
index af34e000f07..a0834b18277 100644
--- a/libgcc/unwind-dw2.h
+++ b/libgcc/unwind-dw2.h
@@ -50,6 +50,12 @@ typedef struct
     } reg[__LIBGCC_DWARF_FRAME_REGISTERS__+1];
     unsigned char how[__LIBGCC_DWARF_FRAME_REGISTERS__+1];
 
+    enum {
+      CFA_UNSET,
+      CFA_REG_OFFSET,
+      CFA_EXP
+    } cfa_how : 8;
+
     /* Used to implement DW_CFA_remember_state.  */
     struct frame_state_reg_info *prev;
 
@@ -58,11 +64,6 @@ typedef struct
     _Unwind_Sword cfa_offset;
     _Unwind_Word cfa_reg;
     const unsigned char *cfa_exp;
-    enum {
-      CFA_UNSET,
-      CFA_REG_OFFSET,
-      CFA_EXP
-    } cfa_how;
   } regs;
 
   /* The PC described by the current frame state.  */

base-commit: 3dfeda095bd43c011fdc3834b9cec39bb9a73a1f